Question

Given : $A=\pi r^2$ and $C=2\pi r$.
Find r in terms of A and C.

• A. $r=\frac{C}{A}$
• B. $r=\frac{2C}{3A}$
• C. $r=\frac{2A}{C}$
• D. None of these
  

Answer 1

Answer: (C)

$r=\frac{2A}{C}$

Given, $A=\pi r^2$ ...(i)
$C=2\pi r$ ...(ii)
On dividing () by (ii), we get
$\frac{A}{C}=\frac{\pi r^2}{2\pi r}$
$\Rightarrow \frac{A}{C}=\frac{r}{2}$
$\Rightarrow r=\frac{2A}{C}$